1. Field of the Invention
The present invention relates to an apparatus for testing infrared cameras, which are installed on a vehicle, for measuring distances to objects, and to a testing method using same.
2. Description of Related Art
A three-dimensional measuring method has been known in the art in which a distance to an object is determined using parallax between a pair of object images taken by a pair of cameras (stereo cameras). In such a method, an apparatus for correcting images must be used in order to accurately measure a distance to an object by correcting shift of images due to distortions of lenses and variations in focal lengths thereof. In an example of such an apparatus, a specific image pattern, such as a regular grid pattern, for measuring an amount of correction is simultaneously taken in advance using both stereo cameras, and the amounts of corrections in the coordinates are calculated pixel by pixel with regard to each image taken by each of the cameras. The calculated results are stored as a correction table for the coordinates, and the data stored in an image memory are corrected pixel by pixel using the correction table for the coordinates so that accurate image data are obtained. In a method disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. Hei 11-325889, the corrections in shifting of images due to distortions of lenses and variations in focal lengths thereof are executed only in the vertical direction.
As an example to which the above-mentioned three-dimensional measuring method using stereo cameras is applied, a system is known which detects obstacles in front of a vehicle earlier than the driver of the vehicle does, and which notifies the driver of the existence of the obstacles. In this case, in general, infrared cameras, which enable taking infrared images, are used as the stereo cameras, in order to aid driving under poor visibility conditions.
As mentioned above, in order to correct shifting of images due to distortions of lenses and variations in focal lengths thereof, a specific image pattern, such as a regular grid pattern, for measuring an amount of correction is simultaneously taken in advance using both stereo cameras, and the amounts of corrections in the coordinates are calculated pixel by pixel with regard to each image taken by each of the cameras; however, in the case of infrared cameras used for the stereo cameras, a problem is encountered in that it is difficult to form a regular grid pattern which can be accurately taken by the infrared cameras.